This year, our group published nine scientific articles related to DNA replication fidelity. We showed that ribonucleotides incorporated during eukaryotic nuclear DNA replication are subject to formation of double strand DNA breaks that result in genome instability. These breaks are due to topoisomerase 1 incision of ribonucleotides incorporated by DNA polymerase epsilon, the primarily leading strand replicase. We collaborated with others to describe the X ray crystal group of DNA polymerase mu bound to a ribonucleotide, and to show that a third divalent metal ion is involved in DNA synthesis by DNA polymerase mu. We also published six review articles.